Two-component injection molds are widely used to manufacture a variety of products. Typical of such products are screw caps for beverage cartons which have reclosable spouts consisting of a polyethylene boss and a polypropylene screw cap. The boss and cap are manufactured in a two-component, or two-shot, injection molding machine. In the first shot, the polyethylene boss is molded as a pre-form. This pre-form then is transferred to the finish injection station, where the second shot or injection of the polypropylene screw cap is made. The composite spout/screw cap then is ejected from the machine as a finished part.
In the past, the majority of two-component injection molding machines transfered the pre-form from the first to the second station for the over-molding by rotating a complete mold half (a rotary machine plate), or rotating part of the ejector-side mold half (indexing plate). In both cases, the pre-form and the finished part are on one parting line, side-by-side. A significant drawback of such a technique is that a large mold clamping area is required; and consequently, it is necessary to use large injection molding machines. Large machines are more costly than small machines, thereby increasing the cost of the finished product.
Two-component injection molding machines of the type described immediately above, while requiring relatively large machines for effecting the operation, still are reasonably practical for molding relatively small parts, such as beverage carton caps of the type described above. For products which have larger dimensions, however, such as toothbrushes which are several inches long, such conventional two-component injection molds require very large injection molding machines because of the relatively long longitudinal dimensions of the toothbrush handles. Several inches are required for each set (the pre-form side and the second shot side), as opposed to only one or two inches (for each part) for beverage carton caps, or the like.
In an effort to reduce the size of the injection molding machine required for two-component molded parts, a mold with a rotating center plate between a fixed plate and a movable plate has been devised. This mold is particularly useful for producing the two-component beverage carton caps described above. When the mold. is closed, the center plate is sandwiched or stacked between the other two plates. The pre-forms are formed between one side of the center plate and one of the other, generally conventional plates. The second shot or completion of the product then is formed between the other side of the center plate and the other one of the conventional plates. The mold then is opened; and the two-component finished products are ejected. The center plate is rotated to place the pre-form parts into position for injection of the second mold, and readying the mold for formation of the pre-forms on the side from which the finished products have been ejected. Each cycle of operation effects a 180xc2x0 rotation of the center plate about its vertical center line (or a center line perpendicular to the movement of the other two plates toward and away from the center plate). The utilization of the rotating center plate, onto which the other two plates are closed and opened, permits the assembly to be placed in a smaller injection molding machine than would otherwise be required to produce the same number of parts in each cycle from a machine using a rotary machine plate or an indexing plate.
Even though the rotating center plate mold described above is an improvement over conventional two-shot molding machines, it still is impractical for use on elongated objects, such as toothbrushes and the like, for the reasons mentioned above in conjunction with the discussion about such products.
Therefore, it is desirable to provide a two-component injection mold for manufacturing two-component elongated products, which may be used with relatively small injection molding machines, and which employs a floating rotatable center plate mounted in a frame between a pair of reciprocating mold plates in which the rotatable mold plate is used to form only a portion of an elongated product to be produced by the mold.
It is an object of this invention to provide an improved two-component injection mold.
It is another object of this invention to provide an improved two-component injection mold using a rotating center plate.
It is an additional object of this invention to provide an improved two-component injection mold using a rotating center plate carried by a floating frame.
It is a further object of this invention to provide an improved two-component injection mold utilizing three mold plates, the central one of which rotates on an axis perpendicular to the opening and closing direction of movement of the mold plates; wherein the rotating mold plate is mounted in an open frame to permit passage of portions of the other mold plates on either side of the rotating plate.
In accordance with a preferred embodiment of this invention, an injection mold for manufacturing two-component elongated members includes first and second mold cavity members mounted for relative movement toward and away from one another in each cycle of operation, to close and open the mold, respectively. A central frame member, designed to overlie at least a portion of each of the first and second mold cavity members when the mold is closed, carries a rotatable mold plate located between a portion of each of the first and second mold cavity members for engagement thereby when the mold is closed. The rotatable mold plate is designed to rotate 180xc2x0 for each closing and opening cycle of the first and second mold cavity members.